FAIR VALUE MEASUREMENT (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of cost aggregate fair value and unrealized holding gains and losses by major security

​	As of December 31, 2015
​	U.S. dollars in thousands
​	Level 1		Level 2		Total
Cash equivalent – Money market funds	​	1,986	​	—	​	1,986
U.S. government treasuries	​	10,874	​	—	​	10,874
Corporate debt securities	​	—	​	309,502	​	309,502
​	​	12,860	​	309,502	​	322,362

​	As of December 31, 2014
​	U.S. dollars in thousands
​	Level 1		Level 2		Total
U.S. government treasuries	​	5,793	​	—	​	5,793
Corporate debt securities (revised from Level 1 classification in the Company’s 2014 annual report to level 2 classification)	​	—	​	27,102	​	27,102
​	​	5,793	​	27,102	​	32,895

Schedule of aggregate fair value and gross unrealized gains and losses by major security

​	As of December 31, 2015
​	Adjusted  Cost		Gross  Unrealized  Gains		Gross  Unrealized  Losses		Aggregate  fair value
​	U.S. dollars in thousands
U.S. government treasuries	​	10,898	​	1	​	25	​	10,874
Corporate debt securities	​	311,253	​	38	​	1,789	​	309,502
​	​	322,151	​	39	​	1,814	​	320,376

​	As of December 31, 2014
​	Adjusted  Cost		Gross  Unrealized  Gains		Gross  Unrealized  Losses		Aggregate  fair value
​	U.S. dollars in thousands
U.S. government treasuries	​	5,794	​	12	​	13	​	5,793
Corporate debentures	​	27,282	​	56	​	236	​	27,102
​	​	33,076	​	68	​	249	​	32,895

Schedule of contractual maturities of investments in available for sale debt securities

​	Fair Value as of  December 31,  2015
Due in 1 year	​	59,394
Due in 2 years	​	91,748
Due in 3 years	​	143,854
Due in 4 years	​	25,380
Due after 4 years	​	—
​	​	320,376